Membrane bioreactor system using reciprocating membrane

ABSTRACT

The present invention relates to membrane bioreactor (“MBR”) system that includes a mechanical membrane reciprocation system to reduce or eliminate membrane fouling. The disclosed MBR system can be operated with higher flux and lower fouling than MBR systems using air scouring. Furthermore the system can remove nitrogen and phosphorous with one RAS and one or no internal recirculation line. The membrane can be reciprocated by a low RPM motor connected to a pulley via belt to rotate rotor to convert rotational motion into reciprocating motion of membrane. Various mechanical means can also be employed to create the reciprocating motion.

RELATED APPLICATION DATA

This application claims priority to application Ser. No. 61/711,081filed on Oct. 8, 2012 and entitled “Vibration Membrane Bioreactor SystemUsing Reciprocating Motion To Treat Wastewater.” The contents of thisapplication are fully incorporated herein.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to a membrane bioreactor (“MBR”) system to treatwastewater. More particularly, the present invention relates to a MBRsystem that employs a repetitive back and forth motion (hereafter calledthe “reciprocating motion” or “reciprocation”) of a submerged membraneto increase filtration and nutrients removal efficiencies instead ofmembrane air scouring which is commonly utilized in submerged MBR.

Description of the Background Art

The background art contains several examples of MBR systems. Thesesystems utilize biological treatment processes (e.g. activated sludgeprocesses) to remove contaminants from wastewater. Several modifiedactivated sludge processes can be used alone or in series for improvedremoval of nutrients in the MBR. Known MBR systems also use low pressuremicrofiltration (MF) or ultrafiltration (UF) membranes as a physicalbarrier for a complete solid-liquid separation. The UF or MF membranescan be submerged in a bioreactor or external to the bioreactor.Submerged membranes are typically installed in an aerobic bioreactor ora separate membrane tank. Membrane air scouring is of utmost importancein submerged MBR operation to prevent severe and rapid membrane fouling.By way of these known techniques, MBR systems can achieve secondary andtertiary wastewater treatment.

One advantage of known MBR systems is the direct production of tertiaryquality effluent with the treatment of domestic or industrialwastewater. Another reason for the growing interest in MBR technology isits smaller footprint compared to conventional treatment processes. Forexample, using conventional MBR systems, a treatment plant couldpotentially double its capacity without increasing its overallfootprint. MBR technology is not only limited to domestic wastewater,but it can also be applied to treat industrial wastewater for reuse.

An example of an MBR system is disclosed in U.S. Pat. No. 4,867,883 toDaigger. This reference discloses a high-rate biological waste watertreatment process for removing organic matter, phosphorus and nitrogennutrients from municipal waste water. A further MBR system is disclosedis U.S. Pat. No. 8,287,733 to Nick et al. It discloses a systemutilizing first and second anoxic basins and first and second aerobicbasins. Also disclosed is the use of a membrane chamber for housing aplurality of membrane tanks.

One common drawback of known MBR systems is membrane fouling. Thisoccurs when soluble and particulate materials accumulate on the membranesurface. When such fouling occurs, there is either a marked decline inpermeate passing through the membrane or an increase in thetransmembrane pressure. In either event, the result is a dramaticreduction in system performance. Membrane fouling is especiallyproblematic in MBR systems given that they generally operate with highermixed liquor suspended solids (“MLSS”).

One solution to membrane fouling is air scouring. Vigorous air scouringallows for stable flux operation without rapid and permanent fouling andespecially cake layer buildup. Given the higher MLSS concentrations atwhich MBR systems operate, frequent maintenance cleanings and out oftank cleanings are also important to maintain membrane performance interms of fouling and permeability. Air scouring is not optimal as it isenergy intensive. In MBR systems energy consumption is considerablyhigher than conventional activated sludge systems due to the additionalair scouring for the membrane.

Thus, there exists a need in the art for improved MBR systems thateliminate or reduce membrane fouling and that do not rely upon airscouring. The present invention is aimed at fulfilling these and otherneeds in the art.

SUMMARY OF THE INVENTION

It is therefore one of the objectives of this invention to reduce oreliminate membrane fouling in an MBR system.

It is a further object of this invention to provide a MBR system thatdoes not utilize membrane air scouring.

It is also one of the objectives of this invention to reduce oreliminate the presence of dissolved oxygen in return activated sludge(RAS) by not utilizing air scouring in membrane tank, thereby permittingthe activated sludge to be returned from a membrane tank to an anoxic oranaerobic treatment tank.

It is still yet another object of this invention to operate MBRs withhigher efficiencies in membrane filtration and biological nutrientsremoval via the reciprocation of a membrane.

The foregoing has outlined rather broadly the more pertinent andimportant features of the present invention in order that the detaileddescription of the invention that follows may be better understood sothat the present contribution to the art can be more fully appreciated.Additional features of the invention will be described hereinafter whichform the subject of the claims of the invention. It should beappreciated by those skilled in the art that the conception and thespecific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings in which:

FIG. 1 is a general process diagram illustrating the MBR system of thepresent invention.

FIG. 2 is a general embodiment of the reciprocation apparatus of thepresent invention.

FIG. 3 is a detailed view of an alternative embodiment of thereciprocation apparatus.

FIGS. 4-12 are process diagrams illustrating various alternative MBRprocesses of the present invention.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

PARTS LIST 10 Influent 20 Mixed Liquor Flow 21 Anaerobic to Anoxic Flow22 Anoxic to Aerobic Flow 23 Aerobic to Membrane Tank Flow 24 Anoxic toAnaerobic Flow 25 Anaerobic to Aerobic Flow 30 Activated Sludge Return31 Activated Sludge Return (Membrane Tank to Anoxic) 32 InternalRecirculation (Anoxic to Anaerobic) 33 Activated Sludge Return (MembraneTank to Anaerobic) 34 Internal Recirculation (Aerobic to Anoxic) 40Effluent 50 Biological Treatment Train 51 Anaerobic Tank 52 Anoxic Tank53 Aerobic Tank 60 Membrane Tank 70 Submerged Membrane, membranecassette 80 Reciprocation Apparatus 90 Sliding Frame 91 Linear Bearingwith Pillow Block 92 Sliding Rail 93 Membrane Cassette Connection Point94 Dampener 100 Rotor 101 Pulley 102 Belt 103 Low RPM motor 110 Shaft

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to membrane bioreactor (“MBR”) system thatincludes a mechanical apparatus for reciprocating a membrane cage (ormembrane cassettes) back and forth. The apparatus eliminates the use ofair scouring. Repetitive reciprocation of the membrane cage/cassettecreates an inertia force acting on the membrane fibers, which shakesfoulants off from the membrane surface. The system includes a membranecage/cassette containing membrane modules that are submerged in eitheran aerobic tank or a separate membrane tank. The membrane cage/cassettecan be mechanically reciprocated via reciprocation apparatus, whichenable the disclosed MBR system to be operated with higher flux andlower fouling than MBR systems using air scoring. Various mechanicalmeans can be employed to create the reciprocating motion. The variousdetails of the present invention, and the manner in which theyinterrelate, are described in greater detail hereinafter.

FIG. 1 illustrates the basic components of the disclosed vibration MBRsystem. The system includes a biological treatment train 50 forreceiving influent 10 to be processed. Various anaerobic, anoxic, andaerobic biological treatment processes can be carried out withintreatment train 50. Mixed liquor 20 from treatment train 50 is thenpassed into membrane tank 60. Membrane tank 60 includes a submergedmembrane 70 (or a series of membranes 70). Membrane(s) 70 may be, forexample, a low pressure microfiltration (MF) or ultrafiltration (UF)membrane used as a physical barrier for a complete solid-liquidseparation. Membrane cage/cassette 70 is mechanically interconnected toa reciprocation apparatus 80. In accordance with the invention,reciprocation apparatus 80 is used in reciprocating membrane 70.Reciprocation apparatus 80, in one non-limiting embodiment, uses amechanical device for converting rotational motion into reciprocatingmotion. Filtration through membrane 70 in membrane tank 60 produceseffluent 40. Membrane 70 may be continually reciprocated duringfiltration. Alternatively, membrane 70 can be selectively reciprocatedas need to eliminate fouling. A portion of the activated sludge 30 (i.e.return activated sludge or “RAS”) goes back to biological treatmenttrain 50 to maintain a sludge concentration within train 50.

FIG. 2 illustrates a general embodiment of the reciprocation apparatus80. Membrane cassette 70 can be connected to a sliding frame 90. Amotorized rotor 100 is connected to a sliding frame 90 via shaft 110.The depicted apparatus 80 thereby converts the rotational motion ofrotor 100 into the reciprocating motion of the sliding frame 90. Thefrequency of reciprocation will be dictated by the speed at which rotor100 is rotated.

An alternative embodiment of such an apparatus is depicted in FIG. 3 andincludes a low RPM motor 103 connected to a pulley 101 via belt 102 torotate rotor 100 to convert rotational motion into reciprocating motionof sliding frame 90 through a shaft 110. Shock load due to reciprocatingmotion can be reduced by dampener 94 in between sliding frame 90 andshaft 110. Sliding frame 90 can move along sliding rail 92 with linearbearing and pillow block 91 supports (FIG. 3). There are many differenttypes of mechanical equipment that can provide the required reciprocalmotion. Those of ordinary skill in the art will appreciate othersuitable mechanical devices after considering the invention.

Various alternative embodiments of the present process invention aredescribed in connection with FIGS. 4-12. With regard to FIG. 4, thesystem consists of a series of biological treatment tanks. These includeanaerobic treatment tank 51, anoxic treatment tank 52, aerobic treatmenttank 53, and membrane tank 60. The membrane 70 is submerged withinmembrane tank 60 and can is reciprocated by reciprocation apparatus 80.

The anaerobic treatment tank 51 receives influent 10 to be treated.Thereafter anaerobic treatment tank 51 biologically treats the influentin the absence of dissolved oxygen to release phosphorous for luxuryuptake in the following aerobic conditions. In anoxic tank 52 thewastewater is denitrified in oxygen-depleted conditions. Dissolvedoxygen is excluded from anoxic tank 52, although chemically bound oxygenmay be present. Nitrification and luxury phosphorous uptake occur in theAerobic treatment tank 53 in the presence of dissolved oxygen.Filtration in the membrane tank 60 produces effluent 40.

There are two recirculation lines for the activated sludge. A line 31delivers return activated sludge (or “RAS”) from membrane tank 60 toanoxic tank 52. Additionally, an internal recycle line 32 delivers aportion of the activated sludge from anoxic tank 52 to anaerobic tank 51to maintain mixed liquor suspended solids (or “MLSS”). In thisinvention, RAS takes two roles in conventional activated sludge or MBRprocesses. In prior art systems, the return flow of activated sludgefrom membrane tank contains dissolved oxygen (“DO”). Thus, in prior artsystems, the activated sludge from the membrane tank could not bereturned to the anoxic 52 or anaerobic 51 tanks due to the high amountsof dissolved oxygen effects on denitrification or phosphorous release.However, with regard the present invention, since physical membranereciprocation is utilized instead of vigorous air bubbling, the DO inthe RAS is minimal compared to conventional MBR. Therefore, only onesludge return line is required for both sludge and nitrate return in thepresent invention.

The system depicted in FIG. 5 includes anoxic 52 and aerobic 53treatment tanks which is similar to the well-known Modified Ludzack andEttinger (MLE) process. As described above, RAS 31 goes to anoxic tank52 directly from membrane tank 60 for nitrate and sludge return in thisinvention. FIG. 6 represents another embodiment which consists of samereactors depicted in FIG. 4. However, return activated sludge 33 goes toanaerobic 51 treatment tank and an internal recycle 34 is made inbetween aerobic 53 and anoxic 52 tanks. FIG. 7 illustrates an embodimentsimilar to the process described in FIG. 6. However, there is nointernal recirculation and the RAS goes to the anoxic tank wheredenitrification occurred. FIGS. 8, 9, 10 and 11 are modified systemsdepicted in FIGS. 4, 5, 6 and 7 respectively. The difference is in theexistence of the membrane tank. The systems in FIGS. 4-7 have a separatemembrane tank 60, but the systems in FIGS. 8-11 do not have a separatemembrane tank 60. Namely, tanks 53 in FIGS. 8-11 function as both amembrane tank and as bioreactor. FIG. 12 shows further example of theprocesses developed in this invention which consists of simplest reactorconfigurations. Reciprocating membrane is submerged in a singlebioreactor where both biological removal and membrane separation occur.The reactor can be aerated tank, pond or sequencing batch reactor (SBR)where aerobic and anoxic conditions are made in cyclic sequence.

The present disclosure includes that contained in the appended claims,as well as that of the foregoing description. Although this inventionhas been described in its preferred form with a certain degree ofparticularity, it is understood that the present disclosure of thepreferred form has been made only by way of example and that numerouschanges in the details of construction and the combination andarrangement of parts may be resorted to without departing from thespirit and scope of the invention.

What is claimed is:
 1. A reciprocating membrane bioreactor systemcomprising: a biological treatment train (50) for receiving influent(10) to be treated, the biological treatment train (50) producingtreated wastewater; a membrane tank (60) housing a membrane (70), thetreated wastewater from the biological treatment train (50) beingfiltered through the membrane (70) to produce effluent (40); areciprocation apparatus (80) for reciprocating the membrane (70), thereciprocation reducing fouling on the membrane (70), wherein thereciprocation apparatus (80) comprises a motor (103) connected to apulley (101) via a belt (102) to rotate a rotor (100) so as to convertrotational motion into reciprocating motion of a sliding frame (90)through a shaft (110), wherein the sliding frame is interconnected tothe membrane so as to move the membrane submerged in the membrane tankin a horizontal reciprocating motion determined by a speed at which therotor rotates.
 2. The reciprocating membrane bioreactor system asdescribed in claim 1 wherein shock load due to reciprocating motion isreduced by a dampener (94) in between the sliding frame (90) and theshaft (110), and wherein the sliding frame (90) is configured to movealong sliding rails with linear bearings and pillow block (91) supports.3. The reciprocating membrane bioreactor system as described in claim 1wherein shock load due to reciprocating motion is reduced by a dampener(94) in between the sliding frame (90) and the shaft (110), and whereinthe sliding frame (90) is configured to move along sliding rails withlinear bearings and pillow block (91) supports.
 4. The reciprocatingmembrane bioreactor system as described in claim 1 wherein thebiological treatment train comprises: an anaerobic treatment tank (51)for biologically treating the influent in the absence of dissolvedoxygen; an anoxic treatment tank (52) for denitrifying the treatedwastewater under oxygen-depleted conditions; an aerobic treatment tank(53) for biologically treating the wastewater in the presence ofdissolved oxygen; and wherein the membrane tank (60) for produceseffluent through the membranes (70) being reciprocated repetitively viathe reciprocation apparatus (80).
 5. The reciprocating membranebioreactor system as described in claim 4 further comprising anactivated sludge return line (31) for delivering the activated sludgefrom the membrane tank (60) to the anoxic treatment tank (52) and aninternal recirculation line (32) from the anoxic tank (52) to theanaerobic tank (51).
 6. The reciprocating membrane bioreactor system asdescribed in claim 4 further comprising an activated sludge return line(33) for delivering the activated sludge from the membrane tank (60) tothe anaerobic treatment tank (51) and an internal recirculation line(34) from the aerobic tank (53) to the anoxic tank (52).
 7. Thereciprocating membrane bioreactor system as described in claim 4 furthercomprising an activated sludge return line (31) for delivering theactivated sludge from the membrane tank (60) to the anoxic treatmenttank (52).
 8. The reciprocating membrane bioreactor system as describedin claim 1 wherein the biological treatment train comprises: an anoxictreatment tank (52) for denitrifying the treated wastewater underoxygen-depleted conditions; an aerobic treatment tank (53) forbiologically treating the wastewater in the presence of dissolvedoxygen; and the membrane tank (60) produces effluent through themembranes (70) being reciprocated repetitively via the reciprocationapparatus (80).
 9. The reciprocating membrane bioreactor system asdescribed in claim 8 further comprising an activated sludge return line(31) that delivers the activated sludge from the membrane tank (60) tothe anoxic treatment tank (52).
 10. The reciprocating membranebioreactor system as described in claim 1 further comprising arecirculation line from the membrane tank (60) to the biologicaltreatment train (50) providing an oxygen-depleted condition.
 11. Areciprocating membrane bioreactor system comprising: a biologicaltreatment train (50) for receiving influent (10) to be treated, thebiological treatment train (50) producing treated wastewater; a membrane(70), the treated wastewater from the biological treatment train (50)being filtered through the membrane (70) to produce effluent (40); areciprocation apparatus (80) for reciprocating the membrane (70), thereciprocation reducing fouling on the membrane (70) and providing oxygendepleted conditions in the biological treatment train (50), wherein thereciprocation apparatus (80) comprises a motor (103) connected to apulley (101) via a belt (102) to rotate a rotor (100) so as to convertrotational motion into reciprocating motion of a sliding frame (90)through a shaft (110), wherein the sliding frame is interconnected tothe membrane so as to move the membrane submerged in a membrane tank ina horizontal reciprocating motion determined by a speed at which therotor rotates.
 12. The reciprocating membrane bioreactor system asdescribed in claim 11, wherein the biological treatment train (50)comprises an aerobic treatment tank (53) for biologically treating thewastewater in the presence of dissolved oxygen.
 13. The reciprocatingmembrane bioreactor system as described in claim 11, wherein thebiological treatment train (50) comprises: an anoxic treatment tank (52)for denitrifying the treated wastewater under oxygen-depletedconditions; an aerobic treatment tank (53) for biologically treating thewastewater in the presence of dissolved oxygen; and an activated sludgereturn line (31) delivers the activated sludge from the aerobictreatment tank (53) to the anoxic treatment tank (52).
 14. Thereciprocating membrane bioreactor system as described in claim 11, thebiological treatment train (50) comprises; an anaerobic treatment tank(51) for biologically treating the influent in the absence of dissolvedoxygen; an anoxic treatment tank (52) for denitrifying the treatedwastewater under oxygen-depleted conditions; an aerobic treatment tank(53) for biologically treating the wastewater in the presence ofdissolved oxygen; an activated sludge return line (31) delivers theactivated sludge from the aerobic treatment tank (53) to the anoxictreatment tank (52); and an internal recirculation line (32) from theanoxic tank (52) to the anaerobic tank (51).
 15. The reciprocatingmembrane bioreactor system as described in claim 11, wherein thebiological treatment train (50) comprises: an anaerobic treatment tank(51) for biologically treating the influent in the absence of dissolvedoxygen; an anoxic treatment tank (52) for denitrifying the treatedwastewater under oxygen-depleted conditions; an aerobic treatment tank(53) for biologically treating the wastewater in the presence ofdissolved oxygen; an activated sludge return line (33) for deliveringthe activated sludge from the aerobic treatment tank (53) to theanaerobic treatment tank (51); and an internal recirculation line (34)from the aerobic tank (53) to the anoxic tank (52).
 16. Thereciprocating membrane bioreactor system as described in claim 11,wherein the biological treatment train (50) comprises: an anoxictreatment tank (52) for denitrifying the treated wastewater underoxygen-depleted conditions; an anaerobic treatment tank (51) forbiologically treating the influent in the absence of dissolved oxygen;an aerobic treatment tank (53) for biologically treating the wastewaterin the presence of dissolved oxygen; and an activated sludge return line(31) delivers the activated sludge from the aerobic treatment tank (53)to the anoxic treatment tank (52).